1. Field of the Invention
The invention relates to a power transmission device suitable for a continuously variable transmission of a vehicle, such as an automobile.
2. Description of the Related Art
There is a known continuously variable transmission for an automobile (power transmission device) (see Japanese Patent Application Publication No. 2000-304115 (JP-A-2000-304115)). The continuously variable transmission includes a primary pulley, a secondary pulley, a looped transmitting member, a casing and a guide rail. The primary pulley is formed of a fixed sheave and a movable sheave, each having a conical sheave surface. The secondary pulley is formed of a fixed sheave and a movable sheave, each having a conical sheave surface. The looped transmitting member is looped over the both pulleys. The casing accommodates these members. The guide rail is supported by the casing, and a string portion of the looped transmitting member is passed through the guide rail so as to be movable relative to the guide rail. Thus, the movement of the looped transmitting member is restricted.
In this type of power transmission device, the portions (string portions) of the looped transmitting member, which are between the pulleys, easily vibrate (string vibrations easily occur) because these portions are not retained by the pulleys. Because these vibrations generate harsh sound (a frequency of approximately 3000 Hz to 4000 Hz), the level of the noise is high. In the power transmission device described in JP-A-2000-304115, string vibrations are reduced by the guide rail supported by the casing. With the power transmission device described in JP-A-2000-304115, string vibrations are reduced. However, the frequency of sound generated due to the string vibrations does not change. Therefore, harsh noise remains. In addition, it is necessary to fit and fix a stabilizer to a fixing stopper. Therefore, further improvement is demanded in order to enhance the ease of assembly and to reduce the cost.